POWER QUALITY
MONITORING
GHASSAN DIB
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Table of Content
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Introduction
Power Quality Parameters
Consequences of Poor Power Quality
System Proposed
Conclusion
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Introduction
What is Power Quality?
Power Quality as a term is often defined as the electrical
network's (grid's) ability to supply a clean and stable power flow
acting as a perfect power supply that is always available, has a
pure noise-free sinusoidal wave shape, and is always within
voltage and frequency tolerances. However, deviations from
these ideal conditions are frequent in most networks as the
number of loads imposing disturbances is increasing rapidly. [1]
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Introduction
Poor Power Quality
Poor power quality is a problem for a wide number of business
sectors and its cost is high and rising as the number of
disturbances is increasing and modern production equipment is
becoming more sensitive to these disturbances. Ironically, it is
often the equipment itself that generates the disturbances. [1]
U.S. companies waste an estimated $26 billion on electrical
power related issues each year.
In EU the waste is around 10 billion euros yearly and the
spending of contra measures is less than 5% of that number.
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Introduction
Causes of Poor Power Quality
Power Quality problems can be traced to three origins – Upstream
supply, internal distribution, or internal loads. [2]
• Internal Distribution
80% of all power quality problems occur in a company’s distribution
and grounding/bonding systems.
Corroded connections, defective conduit, defective electrical devices,
improper wiring, overloading circuits and improper bonding
• Internal Loads
Everything from variable speed drives, microprocessor based devices,
and loads such as lighting and battery chargers contribute to the
resulting quality of electrical power in a circuit. Internal loads can cause
poor power factor, harmonics and power quality events such as sags,
swells, and transients.
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Power Quality Parameters
• The most commonly occurring behaviours that cause
excessive losses and disturbances can be summed up as
follows, to give an idea of where poor power quality arises:
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Reactive power
Harmonics
Network unbalance
Transients (fast disturbances)
Voltage variations (dips, sags, swells, brown-outs)
Flicker
Oscillations (resonances)
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Power Quality Parameters
• A list from the IEC 61000-4-30 Standard:
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Power frequency
Magnitude of the supply voltage
Flicker
Supply voltage dips and swells
Voltage interruptions
Transient voltages
Supply voltage unbalance5
Voltage harmonics
Voltage interharmonics
Mains signalling voltage on the supply voltage
Rapid voltage changes
Measurement of underdeviation and overdeviation parameters
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Power Quality Parameters
Reactive power:
The phase angle between the current and voltage waveforms in an AC
system. Used to develop magnetic field in motors, causes low power
factor. Low reactive power loads up the supply system unnecessary.
The ratio between the active power and the apparent power if often
referred to as the displacement power factor or cos Ø, and gives a
measure of how efficient the utilization of the electrical energy is.
If the cos Ø of the installation is lower than this value, a penalty will be
imposed by the government.
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Power Quality Parameters
Reactive power (Remedy):
If the load is inductive and is relatively steady state, a common
practice is to install contactor switched capacitor banks .
A power factor controller compares the reactive power present in
the network with the target value (e.g. target cos = 0.95) and will
switch on capacitor steps to reach this target
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Power Quality Parameters
Harmonics:
Multiples of the supply frequency, i.e. the fifth harmonic would be
250 Hz if the supply frequency is 50 Hz. Caused by e.g. power
electronic loads such as variable speed drives and UPS systems
Harmonic pollution causes extra stress on the networks and makes
installations run less efficiently.
The harmonic pollution is often characterized by the Total Harmonic
Distortion or THD which is by definition equal to the ratio of the
RMS harmonic content to the fundamental. Typical 5%, for voltage
only, 3%.
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Power Quality Parameters
Harmonics:
Historically passive filters have been and are still being proposed to
mitigate harmonic pollution.
Active filtering (based on power electronics solutions in LV and MV
applications
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Power Quality Parameters
Harmonics
In general, lower frequency harmonics are more serious than higher
frequency, because there is more energy in the lower frequencies.
However, high frequency harmonic distortion can cause problems
with communication and control equipment.
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Power Quality Parameters
Network (Load) unbalance:
Different line voltages. Caused by single-phase loads, phase to
phase loads and unbalanced three-phase loads like welding
equipment.
Load imbalance, especially in office building applications, as the
unbalanced loads may result in excessive voltage imbalance causing
stress on other loads connected to the same network, and leading
to an increase of neutral current and neutral to earth voltage buildup. This can also cause damage to direct online motors by creating a
reverse torque.
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Power Quality Parameters
Transients (fast disturbances):
Rapid change in the sine wave that occurs in both voltage and
current waveforms. Caused by switching devices, start- and stop of
high power equipment.
They can vary widely from twice the normal voltage to several
thousand volts and last from less than a microsecond up to a few
hundredths of a second.
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Power Quality Parameters
Transients (fast disturbances):
• Transients are caused by a rapid release of energy stored
in an inductive or capacitive source in the electrical
system, or from an external source such as lightning.
• While the duration of transients is unnoticeable to a
human observer, their effect on power quality is still
considerable. A single lightning strike can result in a
transient large enough to destroy electronic devices.
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Power Quality Parameters
Voltage variations (dips, sags, swells, brown-outs):
The line voltage is higher or lower than the nominal voltage for a
shorter period. Caused by e.g. network faults, switching of
capacitive loads and excessive loading.
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Power Quality Parameters
Flicker:
Random or repetitive variations in the voltage. Caused by e.g. mills,
EAF operation (arc furnaces), welding equipment and shredders.
Flicker is defined as 'Impression of unsteadiness of visual sensation
induced by a light stimulus whose luminance or spectral distribution
fluctuates with time'. Or in other words, voltage fluctuations on the
supply network cause change of the luminance of lamps, which in
turn can create the visual phenomenon called flicker.
Above a certain threshold it becomes annoying to people present in
a room where the flicker exists. The degree of annoyance grows
very rapidly with the amplitude of the fluctuation.
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Power Quality Parameters
Oscillations (resonances):
The flow of electrical energy, e.g. between the magnetic field of an
inductor and the electric field of a capacitor, changes direction
periodically.
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Consequences of Poor PQ
• Some common direct impacts of poor power quality are:
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Reduced production speed
Charges for reactive power (Penalties imposed by utilities)
Consumption
Lost production
Equipment damage or reduced life time
Idling personnel
Premature equipment aging
Data loss
Start up costs
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Consequences of Poor PQ
• In addition to the direct impacts above, poor power quality
often induces consequential business costs like:
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Postponed revenues
Negative impact on cash flow
Loss of goodwill from customers
Loss of market share
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System Proposed
Ø
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System Proposed
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System Proposed
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Standards
• The new IEC 61000-4-30 CLASS A standard takes the guesswork out of selecting
a power quality instrument.
• The standard IEC 61000-4-30 CLASS A defines the measurement methods for
each power quality parameter to obtain reliable, repeatable and comparable
results. It also defines the accuracy, bandwidth, and minimum set of parameters.
Going forward, manufacturers can begin designing to Class A standards, giving
technicians a level playing field to choose from and increasing their
measurement accuracy, reliability, and efficiency on the job.
• IEC 6100-4-30 Class A standardizes measurements of:
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Power frequency
Supply voltage magnitude
Flicker, harmonics, and inter-harmonics (by reference)
Dips/sags and swells
Interruptions
Supply voltage unbalance
Mains signaling
Rapid voltage changes
• It does not standardize measurements of high frequency transients or currentrelated phenomena.
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Benefits
Additional Benefits
• Building are feed from more than one power source;
example EDL, Own Generator, and Local Generator.
• Thus it important to spot variation in power quality from
these different source so that we take correct decisions;
Retire own generator for a new one or fix it, get power
from a different local generator and maybe run the
institution on local power dropping the EDL (?).
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Benefits
Additional Benefits
• Continuous monitoring of power consumption and later analysis can
lead to identifying operating behaviours causing increased kWh
consumption and reverting them or replacing the method of doing
some things to reduce consumption.
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References
[1]. http://www.comsys.se/solutions/power-quality.html
[2]. www.testersandmeters.com
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